The present invention relates to a generator of periodic signals, in particular for switch-mode power supplies.
As is known, switch-mode power supplies generally employ amplitude modulation (PWM) circuits substantially comprise a voltage comparator which compares a periodic signal with an error signal. Generally said periodic signal is a saw-tooth signal, but in particular applications, for example in vertical switching deflection circuits for the control of a screen, it is necessary to have a signal with exponential raising fronts or edges; this in fact allows to eliminate, or at least attenuate, the cross-over distortion which appears as an intensification of the brightness at the center of the screen.
For the obtainment of periodic signals with such an exponential plot, a discrete device is known comprising a ladder-like circuit including resistors and capacitors. Said known circuit is illustrated by way of example in FIG. 1 and, for an input voltage as illustrated in FIG. 2a, allows to achieve at the output the voltage illustrated in FIG. 2b.
The known solution, however, is not usable in the case of integrated circuits due to the high cost required for its manufacture. In fact it uses two or more capacitors, the integration whereof entails hardly negligible costs, and furthermore, when the capacitors are externally connected, would require the use of at least two pins of the integrated circuit, sometimes requiring the use of larger packages, further increasing the cost of the complete circuit.